The concept of telepresence has been in the public domain since the early 1960s, when Ivan Sutherland demonstrated its basic principles. Two major components of a visual telepresence system are a head mounted display (HMD) and its associated high speed servomechanism on which video cameras are mounted. Two other important components of a visual telepresence system are a head tracker and a communications system linking the HMD with the high-speed servomechanism. When an operator, wearing the HMD, moves her head in any direction, the head tracker senses that movement, sends the appropriate position data to the high-speed servomechanism, which thereby tracks in real-time or in near real-time the operator's head movements. Images from the video cameras mounted on the high-speed servomechanism are transmitted through the communications system to a display positioned in front of the eyes of the operator; for example, such a display forms part of the HMD. As a result, the operator is given a visual impression similar to that from a same location as the remote cameras.
In order to describe this concept more accurately, the term anthropomorphic is often used, whereby a human-shaped configuration is implied. Many systems have been referred to as telepresence systems, for example a camera mounted on a pan and tilt servomechanism controlled by a joystick and in communication with a conventional monitor. This necessitates the use of the term anthropomorphic to provide a more accurate description of human-shaped telepresence wherein the camera is tracking in real-time or near real-time the head and/or eye movement of an operator, and the images thereby gathered by the camera are displayed directly in front of the eyes of the operator.
The use of anthropomorphic visual telepresence is highly advantageous for the operation of remote controlled vehicles. With current advancements in robotic technology the use of remote systems is steadily increasing, especially for performing tasks in hazardous environments where the lives of people are at risk. Hazardous environments are found, for example, in nuclear installations where radiation is a significant concern; in the production and handling of chemicals and explosives; in mining; and in underwater operations such as offshore oil exploration. Further applications include emergency, search and rescue operations, as well as space applications, such as controlling robots and/or vehicles located in the environment of space, while remaining in the safer location of a spacecraft or other human-tended spaceborne habitat. The operator of the remote controlled vehicle is located in a safe place, from which he or she controls the vehicle using other human-machine interface components such as a joystick, while the HMD gives him or her the visual impression of being physically located at a same location as the cameras, which are controlled by the movement of his or her head.
Generally, a telepresence system attempts to recreate an environment for an operator of a remote system. The better the environmental factors are recreated, the more natural the resulting control process is. Of course, because the environmental factors are recreated, the “simulation” is often implemented with safety in mind. For example, radiation levels are not usually simulated other than by showing gauges of sensors within the remote system. In some instances, some environmental factors are altered for providing useful feedback. For example, temperature is raised and lowered to indicate temperature changes, but the simulated temperatures are scaled for operator comfort and safety.
The human visual system is marvelous. From birth, our brain learns to process visual data. The visual data is real-time visual data (for the most part). To clarify, what is seen in a person's hand is felt in their hand at the same time and in the same place. The latency between seeing, feeling and manipulating is truly negligible. This is particularly true of the often occurring situation where a person rotates their head and/or eyes to center an object of interest into the so-called foveal area of the human visual system, from the peripheral area where it was previously located. In such a situation, the brain almost instantly processes new retinal information, and the object of interest is perceived without noticeable delay. Unfortunately, with anthropomorphic visual telepresence systems, this is not so. A small latency of more than a few tens of milliseconds is very noticeable. The brain of an operator of an anthropomorphic visual telepresence system having such a latency is not used to dealing with such a delay. Hence, psycho-physiological discomfort results. Of course, when the latency is negligible these reactions do not occur or are greatly lessened since the brain is operating in its normal mode of operation. It is also clear to those skilled in the art of visual telepresence that latency or time delay between a movement of the HMD worn by the operator, and return of corresponding video images reflecting appropriate movement of the high-speed servomechanism, is a very critical parameter, and that the degree of susceptibility to such latency varies among subjects.
Of course, a similar problem exists with image resolution. The human eye captures images at a high resolution. This resolution is actually variable across the retina, from its maximum in the so-called foveal region to its minimum in the peripheral region. For stationary images, the human brain assembles these images and enhances resolution or accepts the limited resolution presented; however, for moving images, the quantisation—dividing the image into individual points—at a low resolution results in choppy or discretised movement, as opposed to being relatively smooth and continuous as provided by the human visual system. For example, if each square inch of an image is displayed as a single dot, from a location close to the display, a baseball would appear less round and its motion would appear to jump an inch at a time. This also results in psycho-physiological discomfort, such as headaches and nausea, when experienced continuously for extended periods of time. Therefore, it is clear to those skilled in the art of visual telepresence that the resolution of displayed images is of primary importance. It is also well known to those skilled in the art of visual telepresence that video image transmission using analog radio frequency techniques is significantly less robust than video image transmission using digital radio frequency techniques. When using analog video image transmission, frequent interference-induced loss of horizontal and/or vertical synchronization signals may occur. This is significantly reduced when using digitised video image transmission. Loss of synchronization also contributes to psycho-physiological discomfort of an operator wearing the HMD. Therefore, it is often desirable to use digitised video transmission. Unfortunately, this results in a significant increase of the required radio frequency bandwidth for transmission of the video signal. Digital signal compression and decompression, also referred to as CODEC, reduces the required bandwidth but results in added loop latency due to the image processing performed. In situations requiring the use of digitised video image transmission, an anthropomorphic visual telepresence architecture either uses a high transmission bandwidth or suffers the added latency resulting from using the CODEC.
With regards to resolution for applications where colour is required, the implementation of field sequential colour imaging is very successful. In field sequential colour imaging, a colour image is composed of a succession of primary colour components—typically red, green and blue—of the desired image. Several patents have been issued for sequential colour cameras. Similarly, many patents have been issued for sequential colour displays. The field of sequential colour displays is generally a more recent field than that of sequential colour cameras.
It is well known to those skilled in the art of colour image displays that sequential colour displays, when using a sufficiently fast sequential rate so that the human brain will imperceptibly fuse the primary colour images into full colour images, achieve a much higher effective resolution than the more conventionally used composite displays, for which it is implied that the information of all colours is displayed simultaneously instead of sequentially. This is due to the fact that in composite colour displays, a technique must be used in which the available display surface must be subdivided into several primary color groups often referred to as red green blue triads, thus leading to a resolution loss. With sequential colour displays, all of the display's resolution is available for each primary color, as the display's surface does not have to be allocated among the three primary colors.
U.S. Pat. No. 5,684,498 issued Nov. 4, 1997 to Welch et al. describes the use of standard composite colour cameras in conjunction with a sequential colour display forming part of a HMD. This approach leads to colour fringing whenever the HMD is in motion at an appreciable rate. The method described by Welch suppresses colour fringing based on data from rate sensors measuring the motion of the HMD. This method suffers from the inherent inaccuracies of the rate sensors in detection of an acceleration of a head on which the HMD is mounted. Therefore, the image shifting implemented to suppress colour fringing imperfectly corrects for the colour fringing. The method taught by Welch does not achieve a maximum resolution because it uses a composite colour source at its input. Furthermore, the conversion of the composite colour signal into a field sequential colour signal results in additional loop latency.
It is, therefore, an object of this invention to provide an anthropomorphic visual telepresence system having a high resolution and a low loop latency.
It is further an object of this invention to provide an anthropomorphic visual telepresence system enabling, when desired, the use of digital video compression and decompression techniques, while maintaining loop latency within acceptable limits.